OK. The Minuet is lighter than comparable AS, towable by smaller, more fuel efficient vehicles. I would guess the loaded weight of the 6.7 can be kept under 3650 lbs. If maintained before you buy, it will have reasonable upkeep, but keep in mind that it is 30 years old. Appliances are easily replaceable if they break, exterior maintenance is wash and wax as long as the paint is decent, IMHO the aluminum floor will do better if you put a laminate floor in it as aluminum tends to sag a little, and so forth. The axles on older Argosy trailers may need replacement and the front windows need the protection of a rock shield. You DO NOT want to replace one of those wrap windows as they are expensive and available only in gray tint from AS.
I have found my Minuet to be easy to work on, easy to tow, and a good bet to use while you upgrade to whatever you want it to be. My wife and I feel like there is plenty of room for the two of us and we have taken a third person with us with no real difficulty. This 6.7 m is longer than our 6.0 so should be roomier. 6.7 m works out to about 21 - 22 ft, a bit longer than your Safari. Gray water tanks on the Minuets are minimal, about 15 gallons, and the '78 models need a bluetank if you want to shower. '77's are likely the same. '79's have the shower drain into the 15 gallon gray tank so the blue tank is still a good idea there.
As for price, who knows? I have seen the 6.0 Minuets go for $4000 to $8000 in the past two years, but today's financial climate changes things.
Keep in mind that I am a Minuet owner and I am biased toward them. I have owned other AS models and really appreciate not having to use a moose of a truck to tow. My Toyota does fine and gives 12 - 15 mpg towing even in Colorado mountains.
1978 Argosy 6 Metre Minuet
2006 Toyota Tacoma